Semiconductor device

ABSTRACT

A semiconductor device includes a substrate, a semiconductor element disposed on the substrate, a heat radiating plate disposed on the substrate and covering the semiconductor element, and a connection member connecting an upper surface of the semiconductor element and a lower surface of the heat radiating plate, wherein the connection member includes a first member being in contact with the upper surface of the semiconductor element and having a first melting point, a second member being in contact with the first member, having a larger area than the first member, and having a second melting point higher than the first melting point, and a third member interposed between the second member and the heat radiating plate, having an area smaller than the second member, and having a third melting point lower than the second melting point.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of theprior Japanese Patent Application No. 2010-113498, filed on May 17,2010, the entire contents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are related to a semiconductor device.

BACKGROUND

Various semiconductor devices are mounted on an electronic device. Thesemiconductor devices are each formed by mounting a semiconductorelement on a package substrate, and heat generated in the semiconductorelement is released to the outside through a heat radiating plate.

In order to improve the heat radiation effect of the heat radiatingplate, the semiconductor element and the heat radiating plate arepreferably in good thermal connection with each other. Accordingly, astructure is proposed in which the semiconductor element and the heatradiating plate are connected by an alloy with high thermal conductivitysuch as solder, and heat generated in the semiconductor element isefficiently transferred to the heat radiating plate.

In such structure, it is preferable to improve not only the heatradiation effect but also the reliability of the semiconductor device.

Techniques related to the present application are disclosed in JapaneseLaid-open Patent Publication No. 2007-173416 and Japanese Laid-openPatent Publication No. 04-245652.

SUMMARY

According to an aspect of the following disclosure, there is provided asemiconductor device including a substrate, a semiconductor elementdisposed on the substrate, a heat radiating member disposed on thesubstrate and covering the semiconductor element, and a connectionmember connecting an upper surface of the semiconductor element and alower surface of the heat radiating member, wherein the connectionmember includes a first member being in contact with the upper surfaceof the semiconductor element and having a first melting point, a secondmember being in contact with the first member, having a larger area thanthe first member, and having a second melting point higher than thefirst melting point, and a third member interposed between the secondmember and the heat radiating member, having an area smaller than thesecond member, and having a third melting point lower than the secondmelting point.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a semiconductor device used in aresearch;

FIGS. 2A to 2C are enlarged cross-sectional views of the semiconductordevice used in the research during manufacturing;

FIG. 3 is a cross-sectional view drawn based on a microscope image of apackage substrate included in the semiconductor device used in theresearch;

FIG. 4 is a plan view drawn based on a microscope image of the packagesubstrate included in the semiconductor device used in the research;

FIGS. 5A and 5B are cross-sectional views of samples used in anexperiment;

FIGS. 6A to 6C are views drawn based on microscope images of anexperiment sample with a heat radiating plate removed;

FIG. 7 is a cross-sectional view of a semiconductor device in which afirst member and a third member are heated and thereby melted to beconnected to each other with no void being formed in a connectionmember;

FIG. 8 is a cross-sectional view drawn based on a microscope image ofthe semiconductor device in which a second member is covered with thefirst member and the third member;

FIG. 9A is a cross-sectional view of a semiconductor device in which thethicknesses of a first member and a third member are reduced;

FIG. 9B is a cross-sectional view of a semiconductor device in which theentire size of a connection member is reduced;

FIG. 10 is a cross-sectional view for explaining a problem caused by aconnection member with a single-layer structure;

FIG. 11A is a plan view drawn based on a microscope image of a lowersurface of a heat radiating plate;

FIG. 11B is a cross-sectional view drawn based on a microscope image ofthe heat radiating plate and its vicinity;

FIGS. 12A to 12C are cross-sectional views illustrating a cause offormation of a void in the connection member;

FIGS. 13A to 13J are cross-sectional views of a semiconductor deviceaccording to a first embodiment during manufacturing;

FIG. 14 is a perspective view of a connection member used in the firstembodiment;

FIG. 15 is a top view of the semiconductor device according to the firstembodiment;

FIG. 16 is a cross-sectional view for explaining another effect of thesemiconductor device according to the first embodiment;

FIG. 17 is a cross-sectional view for explaining further another effectof the semiconductor device according to the first embodiment;

FIG. 18A is a top view for explaining a method of manufacturing aconnection member according to a first example of a second embodiment;

FIG. 18B is a cross-sectional view taken along a line X2-X2 of FIG. 18A;

FIG. 19 is a perspective view of the connection member manufacturedaccording to the first example of the second embodiment;

FIG. 20A is a plan view of a semiconductor device according to the firstexample of the second embodiment;

FIG. 20B is a cross-sectional view taken along a line X3-X3 of FIG. 20A;

FIG. 21A is a top view for explaining a method of manufacturing aconnection member according to a second example of the secondembodiment;

FIG. 21B is a cross-sectional view taken along a line X4-X4 of FIG. 21A.

FIG. 22 is a perspective view of a connection member manufacturedaccording to the second example of the second embodiment;

FIG. 23A is a plan view of a semiconductor device according to thesecond example of the second embodiment;

FIG. 23B is a cross-sectional view taken along a line X5-X5 of FIG. 23A;

FIG. 24A is a top view for explaining a method of manufacturing aconnection member according to a third embodiment;

FIG. 24B is a cross-sectional view taken along a line X6-X6 of FIG. 24A;

FIG. 25A is perspective view of a lower layer of a connection memberaccording to the third embodiment;

FIG. 25B is perspective view of the connection member according to thethird embodiment;

FIG. 26A is a plan view of a semiconductor device according to the thirdembodiment; and

FIG. 26B is a cross-sectional view taken along a line X7-X7 of FIG. 26A.

DESCRIPTION OF EMBODIMENTS

Before descriptions of embodiments are given, the result of a researchcarried out by the inventors of the present application will bedescribed.

FIG. 1 is a cross-sectional view of a semiconductor device used in theresearch.

This semiconductor device 1 is a ball-grid-array (BGA) typesemiconductor device, and includes a package substrate 2 and asemiconductor element 10.

First electrode pads 3 are provided on one main surface 2 a of thepackage substrate 2. Solder bumps functioning as external connectionterminals 5 are bonded onto the first electrode pads 3, respectively.

Meanwhile, second electrode pads 4 are provided on the other mainsurface 2 b of the package substrate 2. The second electrode pads 4 areelectrically and mechanically connected to electrodes 8 of thesemiconductor element 10 via solder bumps 7, respectively. In order toimprove the connection reliability between the semiconductor element 10and the package substrate 2, underfill resin 11 is filled into a gaptherebetween.

Furthermore, third electrode pads 6 for mounting electronic components14 are provided on the other main surface 2 b of the package substrate2. The electronic components 14 are, for example, chip capacitors, andare soldered to the third electrode pads 6.

The electronic components 14, together with the semiconductor element10, are covered with a metal heat radiating plate 18. The heat radiatingplate 18 serves as a heat radiating member which releases heat generatedin the semiconductor element 10 to the outside, and is bonded to thepackage substrate 2 by adhesive 19.

Here, if a gap exists between the heat radiating plate 18 and thesemiconductor element 10, it is difficult for the heat from thesemiconductor element 10 to be transferred to the heat radiating plate18 due to the heat insulating effect of air in the gap. Thus, the heatradiation effect of the heat radiating plate 18 is deteriorated.

Accordingly, in the semiconductor device 1, an upper surface of thesemiconductor element 10 and a lower surface of the heat radiating plate18 are connected to each other by a metal connection member 16. Thiscauses the heat generated in the semiconductor element 10 to betransferred rapidly to the heat radiating plate 18, and therebyincreases the heat radiation effect of the heat radiating plate 18.

However, when the heat radiating plate 18 and the semiconductor element10 are directly connected to each other by the connection member 16 asdescribed above, stress may be applied to the semiconductor element 10when the heat radiating plate 18 thermally expands. This is due to thedifference in coefficient of thermal expansion between the heatradiating plate 18 and the semiconductor element 10. Such stress maycause a crack in the semiconductor element 10 or may reduce theconnection reliability between the semiconductor element 10 and thepackage substrate 2.

To counter this, in this example, the connection member 16 is formed ofa laminated structure of first to third members 21 to 23. In addition,the second member 22 is made of a deformable metal material having aYoung's modulus smaller than those of the first and third members 21,23, in order to relax the stress applied from the heat radiating plate18 to the semiconductor element 10. For example, high melting pointsolder is used as a material for such second member 22.

Meanwhile, in order that the second member 22 having a role of relaxingthe stress as described above is bonded to the semiconductor element 10and the heat radiating plate 18, the first member 21 and the thirdmember 23 are used. Low melting point solder is used as a material forthe first and third members 21, 23.

Use of the low melting point solder as described above allows the firstand third members 21, 23 to be selectively melted while preventing thesecond member 22 containing the high melting point solder from beingmelted, when the connection member 16 is heated to be bonded to the heatradiating plate 18 and the semiconductor element 10.

As described above, the connection member 16 has a role of relaxing thestress applied from the heat radiating plate 18 to the semiconductorelement 10, in addition to a role of efficiently transferring heat ofthe semiconductor element 10 to the heat radiating plate 18.

However, it has been found out from the research that the connectionmember 16 causes the following problems during the manufacturing of thesemiconductor device 1.

FIGS. 2A to 2C are enlarged cross-sectional views of the semiconductordevice 1 during manufacturing.

In order to manufacture the semiconductor device 1, the connectionmember 16 is disposed between the semiconductor element 10 and the heatradiating plate 18 as illustrated in FIG. 2A, and the connection member16 is heated while the heat radiating plate 18 is pressed by a pressingforce F against the connection member 16.

By this heating, the first and third members 21, 23 containing lowmelting point solder are melted, and spread over the surfaces of thesemiconductor element 10 and the heat radiating plate 18, respectively,while wetting them. Note that, in this step, since the heatingtemperature is lower than the melting point of the second member 22containing the high melting point solder, the second member 22 is notmelted.

Moreover, as illustrated in FIG. 2A, in order to improve the wettabilityof each of the first and third members 21, 23, an Au metallized layer 25may be formed on the upper surface of the semiconductor element 10, anda plating film 26 may be formed on the lower surface of the heatradiating plate 18. The plating film 26 is formed by stacking a Niplating film 51 and an Au plating film 50 on the lower surface of theheat radiating plate 18 in this order.

When the first and third members 21, 23 wet the surfaces and spreadthereon as described above, the first and third members 21, 23 protrudefrom side surfaces 22 a of the second member 22 as illustrated in FIG.2B. Eventually, the first and third members 21, 23 are connected to eachother while taking in the air beside the side surface 22 a, and thus avoid 29 occurs.

As illustrated in FIG. 2C, the void 29 breaksduring the manufacturing ofthe semiconductor device 1, and thus solder particles 30 are scattered.Various causes are conceivable as the cause of the breakage of the void29.

For example, it is conceivable that the void 29 breaks due to thepressing force F applied to the first and third members 21, 23 whenthese members 21, 23 are melted. It is also conceivable that, when heatis applied to the members 21, 23 in a heating step performed after themembers 21, 23 are cooled and solidified, this heat causes the air inthe void 29 to thermally expand, thereby causing breakage of the void29. Such heating step include, for example, a step of reflowing theexternal connection terminals 5 (see FIG. 1) which is performed to mountthe semiconductor device 1 on a mother board, and a step of mounting anelectronic component on the mother board.

FIG. 3 is a cross-sectional view drawn based on a microscope image ofthe semiconductor device in which the void 29 has broken and the solderparticles 30 are scattered as described above.

As illustrated in FIG. 3, the underfill resin 11 is dotted with thesolder particles 30 scattered by the breakage of the void 29.

FIG. 4 is a top view drawn based on a microscope image of the packagesubstrate 2 on which the solder particles 30 are scattered.

As illustrated in FIG. 4, the surface of the package substrate 2 isdotted with the scattered solder particles 30.

If the solder particles 30 attach to terminals 14 a of the electroniccomponents 14 and the like, defects such as electrical short circuitbetween adjacent terminals 14 a occur due to the solder particles 30. Asa result, the reliability of the semiconductor device is reduced.

The inventors of the present application performed the followingexperiment to find out whether the solder particles 30 are actuallyformed by the breakage of the void 29.

In this experiment an experiment sample S1 with a cross-sectionalstructure as illustrated in FIG. 5A was prepared.

In the experiment sample S1, the first member 21 and the third member 23were provided to protrude from the side surface 22 a of the secondmember 22. With such structure, it seems that the first member 21 andthe third member 23 melted by heating are more likely to take in the airbeside the second member 22, and that the void 29 as described above ismore likely to be formed.

Moreover, in this experiment, a reference sample S2 with across-sectional structure as illustrated in FIG. 5B was prepared forcomparison.

In the reference sample S2, the side surfaces of the first to thirdmembers 21 to 23 are aligned with one another. Thus, the referencesample S2 has a structure in which the void 29 is less likely to beformed compared to the experiment sample S1.

Six experiment samples S1 and six reference samples S2 were fabricated.In each of the samples, the first member 21 and the third member 23 wereheated to be melted, and the semiconductor element 10 and the heatradiating plate 18 were thereby connected to each other with theconnection member 16.

Thereafter, the heat radiating plate 18 of each of the samples S1 and S2was removed, and the number of solder particles 30 scattered on thepackage substrate 2 was counted.

As a result, no solder particle 30 was formed in all of the sixreference samples S2.

Meanwhile, formation of the solder particles 30 was observed in five ofthe six experiment samples S1. The probability of the formation of thesolder particles 30 was 83% (=100×⅚) in the experiment samples S1.

Since many solder particles 30 were formed in the experiment samples S1in which the void 29 is more likely to be formed, it was found out thatthe breakage of the void 29 is the cause of the formation of the solderparticles 30.

FIGS. 6A to 6C are views drawn based on microscope images of anexperiment sample S1 with the heat radiating plate 18 removed.

Among these figures, FIG. 6A is a side view, FIG. 6B is across-sectional view, and FIG. 6C is a top view.

As illustrated in FIGS. 6A and 6B, voids 29 are formed in the connectionmember 16 of the experimental sample S1. Furthermore, as illustrated inFIG. 6C, the solder particles 30 are scattered on the package substrate2 of the experimental sample S1.

In the connection member 16 with the structure illustrated in FIG. 1,when the void 29 is formed, a problem of the scattering of the solderparticles 30 occurs. Moreover, even if no void 29 is formed, thefollowing problem occurs.

FIG. 7 is a cross-sectional view of a semiconductor device in which thefirst member 21 and the third member 23 are heated and thereby melted tobe connected to each other with no void 29 being formed.

In this case, the entire surfaces of the second member 22 are cover withthe first member 21 and the third member 23.

FIG. 8 is a cross-sectional view drawn based on a microscope image ofthe semiconductor device in which the second member 22 is covered withthe first member 21 and the third member 23.

The second member 22 has a role of absorbing the stress applied from theheat radiating plate 18 to the semiconductor element 10 by itsdeformation. However, the deformation of the second member 22 isinhibited when the second member 22 is surrounded by the first and thirdmembers 21, 23. Thus, a problem occurs in which the stress relaxingeffect of the second member 22 is reduced, and the connectionreliability between the semiconductor element 10 and the packagesubstrate 2 is reduced.

In order to prevent the first and third members 21, 23 from beingconnected to each other, the following structure is conceivable.

FIG. 9A illustrates a cross section of a structure in which thethicknesses of the respective first member 21 and third member 23 arereduced so that the amounts of the members 21, 23 protruding to the sideof the second member 22 may be reduced.

However, the amounts of the members 21, 23 are small in this structure.Thus, when the semiconductor element 10 and the heat radiating plate 18warp as illustrated in FIG. 9A, it is difficult for the members 21, 23to follow the warping of the semiconductor element 10 and the heatradiating plate 18. As a result, gaps are formed between the connectionmember 16 and the heat radiating plate 18, and between the connectionmember 16 and the semiconductor element 10. Thus, the heat generated inthe semiconductor element 10 is less likely to be effectivelytransferred to the heat radiating plate 18.

FIG. 9B illustrates a cross section of a structure in which the entiresize of the connection member 16 is made smaller than that of FIG. 2A sothat the amounts of the members 21, 23 pushed out to the side of thesecond member 22 may be reduced.

However, with this structure, the Au metallized layer 25 is exposed atthe sides of the connection member 16 by a region by which theconnection member 16 is reduced in size. Thus, the melted first member21 is more likely to wet the exposed Au metallized layer 25 and spreadthereon. As a result, the first member 21 is pushed outward to the sidesof the second member 22. This helps connect the first member 21 and thethird member 23 to each other, and thereby the void 29 is more likely tobe formed.

Moreover, the connection member 16 with a single-layer structure insteadof the three-layer structure as described above is conceivable tosuppress the formation of the void 29.

FIG. 10 is a cross-sectional view for explaining a problem occurring inthe connection member 16 with a single-layer structure.

As illustrated in FIG. 10, in the connection member 16 with thesingle-layer structure, the connection member 16 heated and therebymelted flows out in the lateral direction along the Au plating film 50,and, in a worst case, comes into contact with one of the electroniccomponents 14. In such case, electrical short circuit occurs between theelectronic component 14 and the metal heat radiating plate 18, and thereliability of the semiconductor device 1 is reduced.

FIG. 11A is a view for explaining another problem caused by theconnection member 16 with the single-layer structure, and is a plan viewdrawn based on a microscope image of the lower surface of the heatradiating plate 18.

As illustrated in FIG. 11A, after the connection member 16 is heated andthereby melted, blisters 26 a are sometimes formed in the plating film26 on the lower surface of the heat radiating plate 18. The blisters 26a seem to be formed when moisture taken into the heat radiating plate 18during the fabrication thereof expands due to the heat applied to meltthe connection member 16 and is pooled between the heat radiating plate18 and the Ni plating film 51.

FIG. 11B is a cross-sectional view drawn based on a microscope image ofthe heat radiating plate 18 and its vicinity when the blisters 26 a areformed. Note that, since the plating film 26 is small in thickness, theplating film 26 is not illustrated in FIG. 11B.

As illustrated in FIG. 11B, when the blister 26 a exists in the platingfilm 26, the void 29 is formed in the connection member 16 due to theblister 26 a.

FIGS. 12A to 12C are cross-sectional views illustrating a cause of theformation of the void 29.

As illustrated in FIG. 12A, before the connection member 16 is heatedand thereby melted, the blister 26 a remains in an interface between theNi plating film 51 and the heat radiating plate 18.

Then, as illustrated in FIG. 12B, when the connection member 16 isheated and thereby melted while the heat radiating plate 18 is pressedagainst the connection member 16, the plating film 26 breaks due to thepressing force. As a result, the air inside the blister 26 a moves intothe melted connection member 16, and thus the void 29 is formed in theconnection member 16.

As illustrated in FIG. 12C, the void 29 thus formed causes thescattering of the solder particles 30 as described above.

As described above, it is difficult to completely prevent the formationof the void 29 even with the connection member 16 of single layer.

In view of the above findings, the inventors of the present applicationhave come up with embodiments described blow.

First Embodiment

FIGS. 13A to 13J are cross-sectional views of a semiconductor deviceaccording to this embodiment during manufacturing.

In the description below, a BGA-type semiconductor device ismanufactured as the semiconductor device.

As illustrated in FIG. 13A, to manufacture the semiconductor device, apackage substrate 2 made mainly of an insulating material such asglass-epoxy resin is firstly prepared.

Multiple first electrode pads 3 are provided on one main surface 2 a ofthe package substrate 2. Multiple second electrode pads 4 and multiplethird electrode pads 6 are provided on the other main surface 2 b of thepackage substrate 2. These electrodes 3, 4, 6 are formed by, forexample, pattering copper plating films.

Next, as illustrated in FIG. 13B, solder paste 9 is printed on the thirdelectrode pads 6 by a print process.

Then, as illustrated in FIG. 13C, chip capacitors serving as electroniccomponents 14 are mounted on the solder paste 9, and the solder paste 9is reflowed in this state. Thus, the third electrode pads 6 and theelectronic components 14 are electrically and mechanically connected toeach other.

Subsequently, as illustrated in FIG. 13D, a semiconductor element 10with solder bumps 7 bonded to electrodes 8 is prepared, and the solderbumps 7 are reflowed. Thus, the semiconductor element 10 and the secondelectrode pads 4 are electrically and mechanically connected to eachother.

Note that, an Au metallized layer 25 for improving the wettability of aconnection member described later is formed in advance with a thicknessof about 0.21 μm on an upper surface 10 b of the semiconductor element10.

Thereafter, as illustrated in FIG. 13E, thermosetting underfill resin 11is filled between the package substrate 2 and the semiconductor element10 by using a dispenser 33 in order to prevent reduction in connectionreliability between the package substrate 2 and the semiconductorelement 10, which may possibly occur due to difference in coefficient ofthermal expansion therebetween.

As illustrated in FIG. 13F, after the underfill resin 11 is filled intothe entire gap below the lower surface of the semiconductor element 10,the underfill resin 11 is heated and thereby cured.

Next, a step illustrated in FIG. 13G will be described.

First, a heat radiating plate 18 and a connection member 16 formed bystacking first to third members 21 to 23 are prepared. Among these, theheat radiating plate 18 functions as a heat radiating member whichradiates heat generated in the semiconductor element 10 to the outside,and includes a cavity 18 b to house the semiconductor element 10 and theconnection member 16.

FIG. 14 is a perspective view of the connection member 16.

As illustrated in FIG. 14, each of the first to third members 21 to 23has a substantially rectangular planar shape.

Among the first to third members 21 to 23, the first member 21 is a lowmelting point solder pellet with a thickness of approximately 0.08 μm.

The second member 22 is provided in contact with an upper surface of thefirst member 21. The area of an upper surface 22 y of the second member22 is larger than that of an upper surface 21 y of the first member 21(see FIG. 13G) and that of the upper surface 10 b of the semiconductorelement 10, respectively.

A material of the second member 22 is not limited specifically. In thisembodiment, a high melting point solder pellet with a thickness ofapproximately 0.1 μm is used as the second member 22.

The third member 23 is a low melting point solder pellet with athickness of approximately 0.08 μm, for example. The area of an uppersurface 23 y of the third member 23 is smaller than that of the uppersurface 22 y of the second member 22.

The specific size of each of the first to third members 21 to 23 is notparticularly limited. For example, the first member 21 and the thirdmember 23 are each a square whose length L1 of one side is approximately20 mm, which is substantially the same size as the planar size of thesemiconductor element 10. Furthermore, the second member 22 is a squarewhose length L2 of one side is approximately 24 mm, and has a planersize larger than that of the semiconductor element 10.

Note that, the pellet-shaped members 21 to 23 are not fixedly attachedto each other in this step, and maintain a stacked state with their ownweights.

Table 1 below describes physical properties of high melting point solderusable as the second member 22 and low melting point solder usable asthe first and third members 21, 23.

TABLE 1 Melting Member Material Point Young's Modulus Second Member 22High melting 300° C. 1880 kg/mm² point solder (Sn—95Pb) First and ThirdLow melting 183° C. 3230 kg/mm² Members 21, 23 point solder (Sn—37Pb)

As described in Table 1, the melting point (300° C.) of the high meltingpoint solder (Sn-95Pb) which is the material of the second member 22 ishigher than the melting point (183° C.) of the low melting point solder(Sn-37Pb) which is the material of the first and third members 21, 23.In addition, the high melting point solder has a smaller Young's modulusthan the low melting point solder.

When a material with a small Young's modulus is used as the secondmember 22 as described above, the second member 22 deforms more easilyby stress applied from the outside. Accordingly, the second member 22has a function of relaxing the stress applied to the semiconductorelement 10 due to difference in coefficient of thermal expansion betweenthe heat radiating plate 18 and the semiconductor element 10.

Note that, instead of solder containing lead as described in Table 1,lead-free solder can be used. Tables 2 to 4 below describe examples oflead-free materials usable as the materials for the members 21 to 23.

TABLE 2 Melting Member Material Point Young's Modulus Second Member 22Cu 1083° C. 11250 kg/mm² First and Third Sn—3.5Ag  221° C.  4497 kg/mm²Members 21, 23

TABLE 3 Melting Member Material Point Young's Modulus Second Member 22Cu 1083° C. 11250 kg/mm² First and Third In—3Ag  141° C. In: 1125 kg/mm²Members 21, 23 Ag: 7734 kg/mm²

TABLE 4 Melting Member Material Point Young's Modulus Second Member 22Sn—3.5Ag 221° C. 4497 kg/mm² First and Third In—3Ag 141° C. In: 1125kg/mm² Members 21, 23 Ag: 7734 kg/mm²

Meanwhile, the heat radiating plate 18 of FIG. 13G contains a metal suchas Cu. A plating film 26 is formed on a lower surface 18 a of the heatradiating plate 18. The plating film 26 is formed, for example, bystacking a Ni plating film 51 with a thickness of approximately 4 μm andan Au plating film 50 with a thickness of approximately 0.1 μm in thisorder.

Furthermore, adhesive 19 is provided on the edges of the heat radiatingplate 18 at portions where the heat radiating plate 18 eventually comesinto contact with the package substrate 2.

Next, as illustrated in FIG. 13H, the semiconductor element 10, theconnection member 16, and the heat radiating plate 18 are aligned,respectively, and then stacked one on top of another.

At this point, since the members 21 to 23 of the connection member 16maintain the stacked state with their own weights, it is preferable totake care not to misalign the respective members 21 to 23 when the heatradiating plate 18 is mounted on the connection member 16.

Then, as illustrated in FIG. 13I, the first member 21 and the thirdmember 23 are heated and melted while the heat radiating plate 18 ispressed against the package substrate 2. Thus, the heat radiating plate18 and the semiconductor element 10 are connected to each other via theconnection member 16.

The wettabilities of the melted members 21, 23 are excellent at thistime since the Au metallized layer 25 and the Au plating film 50 areformed respectively on the upper surface of the semiconductor element 10and the lower surface of the heat radiating plate 18 in advance.Accordingly, excellent metal bonding between the first member 21 and theAu metallized layer 25 is achieved. Similarly, excellent metal bondingbetween the third member 23 and the Au plating film 50 is also achieved.

Moreover, since the melted first and third members 21, 23 spread in thelateral direction and the thicknesses thereof are reduced when the heatradiating plate 18 is pressed as described above, the adhesive 19 iseventually brought into contact with the package substrate 2. Thus, theheat radiating plate 18 is bonded to the package substrate 2 via theadhesive 19.

The heating temperature of the connection member 16 in this step is setto be higher than the respective melting points of the first member 21and the third member 23, and is lower than the melting point of thesecond member 22. Thus, in this step, only the first and third members21, 23 can be selectively melted by the heating without the secondmember 22 being melted.

Furthermore, in this embodiment, the area of each of the first and thirdmembers 21, 23 is smaller than the area of the second member 22 asdescribed above. Thus, the melted first and third members 21, 23 areprevented from protruding to a space beside the side surface 22 a of thesecond member 22.

Note that, the thickness ΔT of the connection member 16 after themembers 21, 23 are melted as described above is approximately 0.2 mm.Moreover, the thickness ΔD of the adhesive 19 in a state where the heatradiating plate 18 is bonded to the package substrate 2 is approximately0.5 mm.

The height H from the main surface 2 b of the package substrate 2 to theupper surface of the semiconductor element 10 is approximately 0.61 mm.

Thereafter, as illustrated in FIG. 13J, solder bumps serving as externalconnection terminals 5 are mounted on the first electrode pads 3. Thus,the basic structure of a semiconductor device 40 according to thisembodiment is completed.

FIG. 15 is a top view of the semiconductor device 40. FIG. 13J describedabove is a cross-sectional view taken along a line X1-X1 in FIG. 15.

As illustrated in FIG. 15, the area of the third member 23 is madesmaller than that of the second member 22. Thus, the side surfaces 23 aof the third member 23 are set back from the side surfaces 22 a of thesecond member 22, respectively, by a set back amount ΔL which isapproximately 1 mm.

The electronic components 14 are disposed on the package substrate 2 atpositions beside the side surfaces 22 a from which the side surfaces 23a are set back as described above.

Note that, a land-grid-array (LGA) type semiconductor device may bemanufactured by completing the manufacturing steps of the semiconductordevice without mounting the external connection terminals 5 asillustrated in FIG. 13J.

According to the embodiment described above, the area of each of thefirst and third members 21, 23 is made smaller than that of the secondmember 22 as illustrated in FIG. 13I. Thus, the first and third members21, 23 heated and thereby melted are less likely to protrude to thespace beside the side surface 22 a of the second member 22.

As a result, a void 29 (see FIG. 2B) which may possibly be formed due tothe protruding first and third members 21, 23 is less likely to beformed. Thus, solder particles 30 due to the breakage of the void arenot formed. Accordingly, electrical short circuit between terminals ofthe electronic components 14 due to the solder particles 30 can beprevented, and the reliability of the semiconductor device 40 can beimproved.

In addition, since the protrusion of the first member 21 and the thirdmember 23 is prevented as described above, the second member 22 is notcompletely surrounded by the members 21, 23.

As described above, the second member 22 deforms to relax the stressapplied from the heat radiating plate 18 to the semiconductor element10. Specifically, since the second member 22 is not surrounded by themembers 21, 23 as described above, freedom in movement of the secondmember 22 is secured. Hence, the stress relaxing effect of the secondmember 22 can be maintained.

FIG. 16 is a cross-sectional view for explaining another effect of thisembodiment.

As illustrated in FIG. 10, when the connection member 16 has thesingle-layer structure, there is a risk such that the melted connectionmember 16 comes into contact with the electronic components 14.

In contrast, when the connection member 16 has the three-layer structureas in this embodiment and the area of the third member 23 is madesmaller than that of the second member 22, the second member 22protrudes from the third member 23. In addition, since the melting pointof the second member 22 is higher than that of the third member 23, thesecond member 22 is not melted when the third member 23 is melted.

Thus, the second member 22 functions as eaves which prevent the meltedthird member 23 from dripping down. Hence, the melted third member 23 isprevented from dripping on the electronic components 14, and thereby therisk of electrical short circuit between the terminals of the electroniccomponents 14 is reduced.

Particularly, when the second member 22 is extended so that the sidesurface 22 a thereof may be located above the electronic components 14as illustrated in a dotted line of FIG. 16, the risk of the melted thirdmember 23 dripping on the electronic components 14 can be reduced evenmore effectively.

FIG. 17 is a cross-sectional view for explaining further another effectof the semiconductor device according to this embodiment.

As described with reference to FIGS. 12A to 12C, when the plating film26 is formed on the lower surface of the heat radiating plate 18, thevoid 29 may be formed in the connection member 16 due to blisters 26 ain the plating film 26.

In this embodiment, the side surfaces 22 a of the second member 22protrude from the third member 23 as described above. Therefore, asillustrated in FIG. 17, even if the void 29 breaks and the solderparticles 30 scatter, the second member 22 functions as eaves and thusit prevents the solder particles 30 from attaching to the electroniccomponents 14.

Particularly, when the second member 22 is extended so that the sidesurface 22 a thereof may be located above the electronic components 14as illustrated in a dotted line of FIG. 17, the function of the secondmember 22 as eaves is improved. Hence, scattering of the solderparticles 30 on the electronic components 14 can be suppressed moreeffectively.

Second Embodiment

In the first embodiment, as described with reference to FIG. 14, theconnection member 16 is manufactured in a way that the solder pellets ofdifferent areas are stacked one on top of another and maintain thestacked state with their own weights.

In contrast, in this embodiment, a connection member 16 is manufacturedby pressure bonding solder sheets together, as described below in firstand second examples.

First Example

FIG. 18A is a top view for explaining a method of manufacturing aconnection member 16 according to the first example. FIG. 18B is across-sectional view taken along a line X2-X2 of FIG. 18A.

As illustrated in FIGS. 18A and 18B, in this embodiment, solder sheetswhich serve as first to third members 21 to 23 and are wound aroundfirst to third rolls 41 to 43, respectively, are unwound and pressurebonded by pressure rollers 46, 47. Such pressure-bonded body of soldersheets is also called clad material.

Among the first to third members 21 to 23, a solder sheet with a widthof W1 is used for the first and third members 21, 23, the width W1 beingsmaller than a width W2 of a solder sheet used for the second member 22.

After the clad material of the first to third members 21 to 23 is formedas described above, the clad material is cut into pieces by a cutter 49.Thus, a plurality of connection members 16 are manufactured.

FIG. 19 is a perspective view of the connection member 16 manufacturedin the above manner.

In this embodiment, since each of the connection members 16 ismanufactured by cutting the clad material, the respective side surfacesof the respective first to third members 21 to 23 exist on the sameplane in each of cut surface 16 x of the connection members 16.

Among four sides of the rectangular third member 23, only side surfaces23 a at two sides thereof are set back from corresponding side surfaces22 a of the second member 22, the two sides not existing in the cutsurfaces 16 x and being on the opposite sides.

FIG. 20A is a plan view of a semiconductor device provided with theconnection members 16, and FIG. 20B is a cross-sectional view takenalong a line X3-X3 of FIG. 20A.

As illustrated in FIGS. 20A and 20B, electronic components 14 areprovided on a package substrate 2 at positions beside the set-back sidesurfaces 23 a of the third member 23.

This configuration causes the second member 22 protruding from the sidesurfaces 23 a to function as eaves which prevent solder particles fromattaching to the electronic components 14. Therefore, as similar to thefirst embodiment, it is capable of preventing electrical short circuitbetween terminals of the electronic components 14 due to the solderparticles.

In addition, no electrical component 14 is provided beside the cutsurfaces 16 x of the connection member 16. Thus, even when a void 29 isformed in any of the cut surfaces 16 x and thus solder particles 30 areformed, the solder particles 30 do not attach to the electroniccomponents 14.

According to this example described above, the connection members 16 aremanufactured by cutting the clad material formed by press bonding threelayers of solder sheets. Accordingly, since the respective members 21 to23 in each connection member 16 are press bonded to each other, themembers 21 to 23 are not misaligned from one another during the process,unlike the case where the members 21 to 23 are manufactured from pelletmaterials and maintain the stacked state only with their own weights.Thus, there is no need to align the members 21 to 23 when the connectionmember 16 is mounted on the semiconductor element 10, and the workefficiency is improved compared to the first embodiment.

Second Example

FIG. 21A is a top view for explaining a method of manufacturing aconnection member 16 according to the second example. FIG. 21B is across-sectional view taken along a line X4-X4 of FIG. 21A. Note that, inthese drawings, components same as those described in the first exampleare denoted with the same reference numeral as the first example, anddescriptions thereof are omitted.

In this example, as illustrated in FIG. 21A, a solder sheet with a widthof W1 is used for first and third members 21, 23, the width W1 beingsmaller than a width W2 of a solder sheet used for a second member 22.

The first to third members 21 to 23 are press bonded to form a cladmaterial while respective one sides 21 b to 23 b of the respective firstto third members 21 to 23 are aligned to one another. Then, the cladmaterial is cut by a cutter 49 to form a plurality of connection members16.

FIG. 22 is a perspective view of the connection member 16 manufacturedin the above manner.

In this embodiment, the clad material is cut while the respective onesides 21 b to 23 b of the respective first to third members 21 to 23 arealigned to one another as described above. Thus, only a side surface 23a, of the rectangular third member 23, at the other side opposite to theone side 23 b is set back from a side surface 22 a of the second member22.

FIG. 23A is a plan view of a semiconductor device including thisconnection member 16. FIG. 23B is a cross-sectional view taken along aline X5-X5 of FIG. 23A.

As illustrated in FIGS. 23A and 23B, electronic components 14 areprovided on a package substrate 2 at positions beside the set-back sidesurface 23 a of the third member 23, and are not provided in otherregions. Thus, the second member 22 functions as eaves for theelectronic components 14, and it is possible to reduce a risk such thatsolder particles scatter on the electronic components 14.

In this example described above, the connection members 16 aremanufactured from the clad material as similar to the first example.Thus, the workability is improved compared to a case where all of themembers 21 to 23 are manufactured from pellet materials.

Third Embodiment

In the second embodiment, the connection members 16 are manufacturedusing the clad material formed of three layers of solder sheets.

Instead, in this embodiment, connection members 16 are manufacturedusing both a clad material and solder pellets as described below.

FIG. 24A is a top view for explaining a method of manufacturing aconnection member 16 according to this embodiment. FIG. 24B is across-sectional view taken along a line X6-X6 of FIG. 24A. Note that, inthese drawings, components same as those described in the secondembodiment are denoted with the same reference numeral as the secondembodiment, and descriptions thereof are omitted.

The connection members 16 are manufactured as follows. As illustrated inFIGS. 24A and 24B, solder sheets which serve as first and second members21 and 22 and are wound around rolls 41 and 42, respectively, areunwound and press bonded by pressure rollers 46, 47 to form a cladmaterial with a two-layer structure.

In this embodiment, these first and second members 21, 22 have the samewidth W3.

The clad material with a two-layer structure is cut by a cutter 49 toform lower layers 16 b of the respective connection members 16 having asubstantially rectangular planar shape.

FIG. 25A is perspective view of a lower layer 16 b manufactured in theabove manner.

Thereafter, as illustrated in FIG. 25B, a low melting point solderpellet which serves as a third member 23 and which has a substantiallyrectangular planar shape is stacked on each of the lower layers 16 b atits center, and thus the connection member 16 is completed.

The third member 23 has a smaller area than the second member 22, andside surfaces 23 a at four sides of the rectangular third member 23 areset back from side surfaces 22 a of the second member 22, respectively.Note that, the third member 23 maintains a state of being mounted on thesecond member 22 simply by its own weight, and the members 22, 23 arenot press bonded to each other as in the clad material.

FIG. 26A is a plan view of a semiconductor device including thisconnection member 16. FIG. 26B is a cross-sectional view taken along aline X7-X7 of FIG. 26A.

As illustrated in FIGS. 26A and 26B, the first member 21 and the secondmember 22 are provided to extend to positions above the electroniccomponents 14 and to cover the electronic components 14.

In this embodiment described above, the lower layer 16 b of theconnection member 16 is manufactured from the clad material, and thethird member 23 is manufactured from the solder pellet.

Accordingly, when the connection member 16 is manufactured, there is aneed to perform only the alignment between the lower layer 16 b and thethird member 23, and there is no need to align all of the first to thirdmembers 21 to 23 unlike the case of manufacturing all of the first tothird members 21 to 23 from solder pellets. Thus, the workability isexcellent.

Furthermore, as illustrated in FIG. 26B, the second member 22 isprovided to cover the electronic components 14. Thus, even when blisters26 a (see FIG. 12A) exist in a plating film 26, solder particles formedby the breakage of the blisters can be prevented from scattering on theelectronic components 14. This configuration reduces a risk ofelectrical short circuit between terminals of the electronic components14 due to the solder particles, and thus improves the reliability of thesemiconductor device.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the inventionand the concepts contributed by the inventor to furthering the art, andare to be construed as being without limitation to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although the embodiments of the presentinventions have been described in detail, it should be understood thatthe various changes, substitutions, and alterations could be made heretowithout departing from the spirit and scope of the invention.

1. A semiconductor device comprising: a substrate; a semiconductorelement disposed over the substrate; a heat radiating member disposedover the substrate and covering the semiconductor element; and aconnection member connecting an upper surface of the semiconductorelement and a lower surface of the heat radiating member, wherein theconnection member includes: a first member being in contact with theupper surface of the semiconductor element and having a first meltingpoint; a second member being in contact with the first member, having alarger area than the first member, and having a second melting pointhigher than the first melting point; and a third member interposedbetween the second member and the heat radiating member, having an areasmaller than the second member, and having a third melting point lowerthan the second melting point.
 2. The semiconductor device according toclaim 1, wherein the first member and the third member are made of lowmelting point solder, and the second member is made of high meltingpoint solder.
 3. The semiconductor device according to claim 1, whereinthe first member and the third member are made of Sn-37Pb solder, andthe second member is made of Sn-95Pb solder.
 4. The semiconductor deviceaccording to claim 1, wherein an Au metallized layer is formed over theupper surface of the semiconductor element, and a surface of the heatradiating member in contact with the connection member is plated withAu.
 5. The semiconductor device according to claim 1, wherein a planarshape of each of the first member, the second member, and the thirdmember is a rectangle.
 6. The semiconductor device according to claim 5,wherein a side surface of the third member is set back from a sidesurface of the second member at least one side of the rectangles, and anelectronic component is disposed on the substrate at a position besidethe set-back side surface of the third member.
 7. The semiconductordevice according to claim 6, wherein the side surface of the thirdmember is set back from the side surface of the second member only attwo sides opposite to each other among the four sides of the rectangles.8. The semiconductor device according to claim 6, wherein the sidesurface of the third member is set back from the side surface of thesecond member only at one side of the rectangles.
 9. The semiconductordevice according to claim 6, wherein the side surface of the secondmember is located above the electronic component.
 10. The semiconductordevice according to claim 6, wherein the second member covers theelectronic component.